WO1988002762A1

WO1988002762A1 - Vinyl chloride polymer products

Info

Publication number: WO1988002762A1
Application number: PCT/EP1987/000572
Authority: WO
Inventors: Jean Riviere; Eduard Andries Wokke
Original assignee: Dunlop-Cct S.A.
Priority date: 1986-10-08
Filing date: 1987-10-06
Publication date: 1988-04-21
Also published as: EP0286659A1; CN87107070A; ZA877495B; ES2008257A6; PL268097A1; AU8036487A; GB8624082D0; JPH01501554A; KR880701757A

Abstract

Products having high thermal stability and flame retardancy are obtained by curing a vinyl chloride polymer composition containing a phosphate plasticizer and a 2-substituted-4,6-dithiol-s-triazine and/or a salt thereof. Moulded products, for example polymer-impregnated belting carcasses, may be demoulded at relatively high temperatures.

Description

VINYL CHLORIDE POLYMER PRODUCTS This invention relates to the production of vinyl chloride polymer products, particularly to products in which the vinyl chloride polymer is cured using a s-triazme derivative having at least two thiol substituent and/or a salt of such a derivative, and to compositions suitable for making such products.

The existence of plasticized non-curable (non-crosslmkable) vinyl chloride compositions, also known as plastisols, is well known.

Also, more recently it has been proposed that certain chlonne- containing polymers may be crosslmked by means of certain thiol-substitut s-triazmes. For instance, United Kingdom Patent Specification No. 151226 relates to the use of 2-substιtuted-4,6-dιthιol-s-trιazιnes and metal salt thereof to crosslink vinyl chloride polymer resins. In that Specification the piasticizer advocated in all of the illustrative experiments is dioctyl phthalate; no other particular plasticizers are specified.

An object of the present invention is to provide a curable (cross- linkable) vinyl chloride polymer composition which can be heat-cured to produce a product having a high flame retardancy coupled with high tnermal stability, solvent-resistance and strength. Also, in relation to the production of moulded products from curable vinyl chloride polymer compositions, an object of the invention is to reduce or eliminate the cooling stage which often is necessary prior to de-moulding, and thereby to save time and expense in commercial production, without detriment to the product. One utilisation of this invention relates to fibre-reinforced products, for example mechanical belting, especially conveyor belting, and particularly to the carcass thereof.

Mechanical belting typically has a basic structure of a carcass consisting primarily of a textile component embedded in or impregnated with a plastics, resin or rubber, to provide tensile strength, and a cover material of a plastics or rubber to protect the carcass and to provide a surface for transmitting the drive force on the belting. One form of mechanical belting is conveyor belting, which usually is in laminar sheet form, for conveying materials to be treated or transported. The present invention is especially applicable to conveyor belting having a carcass of synthetic and/or natural textile fibre in a polymer composition of which the polymer component consists at least partially of a vinyl chloride polymer and which is consolidated by curing to achieve 2. dimensional stability. Normally in the production of such belting it has been necessary to include a cooling stage after curing, especially after press-curing, to reduce the temperature of the consolidated assembly to about 55°C prior to removal from the mould or press in order to avoid the risk of damage to the assembly by fluxing of the composition. By means of the present invention, it is possible to reduce or eliminate this cooling stage without detriment to the resultant belting and, moreov to produce belting having an advantageously high flame retardancy and other advantageous properties. The present invention also may be utilised advantageously in the production of other vinyl chloride polymer products for which thermal stability and flame retardancy are desirable. One such group of products comprises floor coverings and other surface coverings.

In addition to high thermal stability and a high flame retardancy, products made in accordance with the invention usually have a high resistance to attack by organic solvents, oils and the like, a high ageing resistance owing to inhibited migration of piasticizer, a high strength and good low-temperature properties (especially retention of elastomeric properties). Also, the curable compositions of the invention usually have high cure efficiency.

Moreover, particular advantages may be attained by means of preferred embodiments of the invention as described hereinafter.

According to the present invention there is provided a curable vinyl chloride polymer composition comprising a phosphate piasticizer and a triazine derivative selected from 2-substituted-4,6-dithiol-s-triazines and salts thereof.

According to the present invention also there is provided a cured<> vinyl chloride polymer product made by a method comprising subjecting the aforesaid composition to curing conditions. According to one aspect of the present invention there is provided a method of making a moulded product, comprising heating the aforesaid composition in a mould to cure the composition and removing the cured moulded composition from the mould at a temperature of at least 60°C.

According to a further, more particular, aspect of the present invention there is provided a mechanical belting carcass comprising textile fibre and the aforesaid vinyl chloride polymer composition which has been cured in a mould and removed therefrom as defined above.

The vinyl chloride polymer for use in the present invention may be poly(vinyl chloride) or a copolymer of vinyl chloride with, for example, vinyl acetate or vinylidene chloride. The vinyl chloride polymer may be the sole polymer component of the composition or the composition may include one or more additional polymers, for example a rubber such as a butadiene/acrylonitrile, polychloroprene or natural rubber. The triazine derivative employed as the curative in the present invention preferably should be able to co-cure the vinyl chloride polymer and the rubber.

The curable composition may be employed as a paste or plastisol comprising microsuspended or emulsified vinyl chloride polymer. In addition to the microsuspended or emulsified polymer, the composition can include a filler of solid particles of vinyl chloride polymer such as pol (vinyl chloride) or a copolymer of vinyl chloride and vinyl " acetate. Such a filler suitably has a mean particle size of less than 60 u and may be present in an amount of, for example, up to 30 parts by weight per 100 parts by weight of microsuspended vinyl chloride polymer.

The triazine derivative usually is in the form of a water-insoluble non-flammable powder. A preferred 2- substituent in the triazine • derivative is a further thiol (-SH) group or a tertiary amino substituent, especially dibutylamino (-N(C.H_),-,) . Examples of other suitable tertiary amino substituents include -NHCgH₅, -NCC^)-, - (CH₃)₂ and -NfCH-CgH-)-, and an example of an alternative substituent is -OCgH-. A preferred salt of the triazine derivative is the magnesium salt, which may be produced in situ in the vinyl chloride polymer composition. Examples of alternativ salts include other metal salts such as the monosodium, disodium, mono- potassium, dipotassium, calcium and barium salts, onium salts and quinine salts. A suitable amount of triazine derivative or salt thereof is in the range 2 to 6 parts by weight per 100 parts by weight of vinyl chloride polymer. The phosphate piasticizer may have alkyl and/or aryl and/or alkaryl groups. Especially suitable plasticizers have at least two aryl and/or alkaryl groups. Examples are isopropylated triaryl phosphate, diphenyl cresyl phosphate and octyl diphenyl phosphate. It is found that, in the present invention, phosphate plasticizers result in an unexpected higher cure efficiency than do non-phosphate plasticizers such as alkyl phthalates and alkyl sulphonic esters of phenol and cresol, and confer an unexpected high level of flame retardancy on the cured product.

If desired, a phosphate piasticizer may be employed together with one or more non-phosphate, plasticizers, and in some cases, for instance when a low viscosity composition is desirable, such a piasticizer combination may be preferred. A suitable piasticizer combination is found to be a phosphate:non-phosphate (for example an alkyl phthalate) piasticizer weight ratio in the range 95:5 to 80:20, depending on the final properties required. Such a combination normally produces low viscosity compositions which may be cured to a high degree (such as substantially lQ0_) even with relatively small proportions of triazine derivative, an confers a high level of flame retardancy. A suitable total amount of piasticizer may be in the range 40 to 120 parts by weight per 100 parts by weight of vinyl chloride polymer.

The vinyl chloride polymer composition often may include a basic metal compound such as an oxide, carbonate or carboxylate (e g caprylate) of a metal such as magnesium, calcium, barium, zinc, tin or lead, to activate the curing of the polymer and to accept the halogen atoms eliminated from the polymer. A preferred metal compound is magnesium oxide. The amount of metal compound employed suitably is in the range 2 to 10 parts by weight per 100 parts by weight of vinyl chloride polymer. However, it is found unexpectedly that an advantageous flame- retardant cured product may be obtained without the presence of a basic metal compound such as MgO when the s-triazine derivative is 2,4,6- trithiol-s-triazine, particularly when an organo-tin stabiliser, especially an alkyl-tin stabiliser (e g a butyl-tin stabiliser), is present. It is believed that there is a synergistic coupling system effect between the trithiol-s-triazine, the phosphate piasticizer and the organo-tin stabiliser. A suitable amount of organo-tin stabiliser may be in the range 0.5 to 8 parts by weight, especially 4 to 6 parts , by weight, per 100 parts by weight of vinyl chloride polymer. 0 If desired, one or more solid flame-retardants may be included in the compositiαi. Examples of such flame-retardants are antimony trioxide and alumina trihydrate. An example of a suitable amount of solid flame- retardant is up to 30 parts by weight, for instance up to 15 parts by weight, per 100 parts by weight of vinyl chloride polymer. Compositions 5 of.the invention containing a solid flame-retardant are found to exhibit a particularly high level of flame-retardancy, synergistically.

In some cases it is preferable to include an onium salt in the composition. Onium salts may act as solid-liquid phase transfer catalysts. Suitable onium salts may be represented by the formulae. Q⁺ X^~ and Q X^n~ wherein Q = quaternary ammonium, arsoniu or phos- phonium, n = at least 2, and X = a monovalent anion e g Cl, Br, I or HSO. or a polyvalent anion e g SO.. Examples of suitable onium salts 5 are CgH₅CH₂(C.H_g)₃P⁺Cl~, (R)₄N⁺Br~ where R = hydrocarbon or alkyl ether, and the onium sulphate available under the trade name EL 1628 or Atmer 160 ex. ICI. The onium salt reacts with the metal salt of the triazine derivative to produce the onium salt of the triazine derivative and the metal salt having the onium salt anion. The efficiency of this 10 reaction increases as the solubility of the metal salt having the onium salt anion decreases in relation to the solubility of the metal salt of the triazine derivative. Best results are achieved when the solubility of the metal salt of the triazine derivative is greater than the solubili of the metal salt having the onium salt anion. The onium salt of the 15 triazine derivative may have a greater curing efficiency than does the metal salt of .the triazine derivative, and it may confer an antistatic property. An example of a suitable range of amounts of onium salt in the composition is from 0.5 to 3 parts by weight per 100 parts by weight of vinyl chloride polymer. However, if a relatively high proportion of 20. onium salt is employed, such as 2 to 3 parts by weight per 100 parts by weight of vinyl chloride polymer, it might increase the viscosity and reduce the thermal stability of the composition. Accordingly, a relatively small, catalytic, proportion of onium salt may be preferable, for example about 0.5 to 1 part by weight per 100 parts by weight of 5 vinyl chloride polymer.

The composition may also include a polyethyleneglycol or an alkyl ether derivative thereof such as butyl carbitol or triethylene glycol monomethyl ether. Such an ingredient may accelerate the cure of the vinyl chloride polymer by acting as a co-ordinating agent for the metal 0 cations in the composition. A suitable amount of this ingredient is in the range 2 to 10 parts by weight per 100 parts by weight of vinyl chloride polymer.

The present invention may be utilised to produce cellular (including porous) products by including a cell- (or pore-) forming 5 ingredient in the composition. For instance a chemical blowing agent such as azodicarbonamide may be employed. By way of example only, a suitable amount of azodicarbonamide blowing agent is about 2 parts by weight per 100 parts by weight of vinyl chloride polymer. Cellular

6. products in accordance with the invention may be useful for flame retardant cushioning applications, for instance floor and other surface coverings.

Examples of further optional ingredients in the composition include liquid flame-retardants (e g chlorinated paraffins and halogenophosphates), inorganic fillers (e g titanium dioxide) , viscosity depressants (e g N-iuryl benzene sulphonamide, non-ionic fatty acid esters and derivatives thereof) and co-stabilisers (e g epoxidised soya oil) . An inorganic filler may be present in an amount of, for example, 0.5 to 8 parts by weight per 100 parts by weight of vinyl chloride polymer.

The composition may be prepared by conventional mixing techniques. In some cases, especially when a relatively viscous piasticizer is employed, it may be preferable to produce the composition by first mixing together all of the ingredients except the vinyl chloride polymer using a vigorous mixing technique and then to add the vinyl chloride polymer incrementally using a less vigorous technique, in order to achieve the desired solution of the triazine derivative in the composition. Solid filler particles of vinyl chloride polymer may be added incre¬ mentally or, when a relatively small proportion of such particles is employed, such as less than 20 parts by weight per 100 parts by weight of microsuspended or emulsified vinyl chloride polymer, they may be added in bulk.

As referred to above, an advantageous utilisation of the invention is in the production of fibre-reinforced vinyl chloride polymer products such as mechanical belting, especially conveyor belting. The textile fibre of the belting carcass usually is in the form of one or more woven and/or knitted fabric plies, and a preferred carcass for conveyor belting comprises two or more fabric plies which may be the same or different, connected together by interwoven threads, usually warp threads, which may or may not be constituents of one or more of the plies. Such an interconnected fabric is known as solid-woven fabric. For strength, the fabric usually consists solely or mainly of synthetic fibre, typical fibrous materials being polyester, polyamide and poly- aramid. However, if desired, the fabric may include natural fibre such as cotton or rayon, for example to provide bulk and/or to protect the belting from damage in use. Also if desired, the carcass may include one or more additional components such as metal reinforcements.

The vinyl chloride polymer suitably is applied to the textile fibre in the form of a paste or plastisol, typically by impregnation such as by dipping, and usually the assembly is heated in a press to cure the polymer and consolidate the assembly to increase the dimensional stabilit of the carcass. Preferably the polymer paste has a low viscosity in orde to attain a high level and efficiency of impregnation. A preferred past viscosity is in the range 3000 to 8000 mPa.s at a shear rate D of 10 s~ at 20°C, and a suitable technique for obtaining the desired low viscosity is to use a polymer of the microsuspension or emulsion type.

After the polymer composition has been applied to the textile fibre, usually it is pre-gelled, such as by heating in the range of about 80°C to 150°C for about 10 minutes, to solidify the composition without attaining its maximum mechanical properties, and subsequently the composition is subjected to final curing conditions after assembly with other components of the belting such as the cover material. Typically the curing conditions include heating the assembly at a temperature of at least about 160°C in a press or mould. The operating pressure during the curing stage may be, for example, in the range 10 to 35 kg/cm². The cover material may be chosen depending on the use of the belting and usually is of rubber or plastics material. A rubber cover suitably is applied by calendering onto the carcass containing the pre-gelled polymer composition. If desired, an intermediate layer of a mutually compatible rubber composition may be applied between the carcass and the rubber cover to r__urcrt_e adhesion between them. A preferred plastics cover is a vinyl chloride polymer and this may be applied in the form of a pseudoplastic paste of higher viscosity than that of the impregnant, followed by pre-gelling at about 80°C to 150°C and then subjecting the assembly to the curing conditions.

In contrast to the use of conventional vinyl chloride polymer paste compositions, the cured product in accordance with the present invention normally can be removed from a mould or press at a relatively high temperature of at least 60°C and may be at least 120°C and up to about 180°C or even higher, without harm. Also, it is found that cured products in accordance with the invention may have a maximum temperature of less than 270°C in the standard Drum Friction Test according to CEE and NCB specifications. Moreover, it is found that the curing of the vinyl chloride polymer occurs substantially entirely in the polymer gel state; substantially no curing occurs during preparation of the composition or during the pre-gelling step. The invention is illustrated, by way of example only, in the following Examples. In these Examples, the usual procedure employed to make the vinyl chloride polymer compositions was as follows. All of the ingredients except the vinyl chloride polymer(s) were blended together, the vinyl chloride/vinyl acetate copolymer 'VC/VA' (if employed) was then introduced and then the poly(vinyl chloride) 'PVC was added incrementally with medium mixing rate. After addition of all ingredients the composition usually was subjected to final mixing for about 3 minutes. EXAMPLE I

Paste compositions were prepared from the following formulations:

I.a I.b I.c I.d I.e

(parts by weight)

PVC microsuspension 80 80 80 80 80 (Vestolit B 7021)

VC/VA containing 1% VA 20 20 20 20 20 ^'

(Hostalit SA VP 1062/7)

Alkyl sulphonic ester of phenol 30 30 30 30 0 and cresol (Mesamoll)

^C7^~C11 ^dialkY¹ Phthalate 30 30 30 30 0 (Santicizer 711)

Isopropylated triaryl phosphate 0 0 0 0 60 (Reofos 50)

Butyl-tin stabiliser 2 2 2 2 2

(Lankro LT 63)

MgO 0 2 2 4 2

2-dxbutylamino-4,6-dithiol- 0 1 2 2 2 s-triazine

Viscosity at Shear Rate D of 3200 3600 4200 5400 11200

10 s (mPa.s) The compositions were pre-gelled by heating at 100°C for 10 minutes and were cured in a mould under a pressure of 30 kg/cm² at 170°C for 10 minutes. The cured compositions were removed from the mould at 150°C.

The level of cure was determined by measuring the % Swelling in tetrahydrofuran (using a Soxhlet apparatus) and the % Gel remaining after removal of the tetrahydrofuran solution and drying. The results were as follows:

I.a I.b I.c I.d I.e % Swelling dissolves - +240 +310 +453

% Gel 0 16 50 100 100 This Example shows that the piasticizer consisting of equal proportions of phthalate and sulphonic ester requires the presence of a higher amount of MgO than does the phosphate piasticizer to attain

100% cure, and that the phosphate piasticizer produces a much higher viscosity composition.

EXAMPLE II

Paste compositions were prepared from the following formulations:

II.a II.b

(parts by weight) PVC microsuspension 80 80

(Vestolit B 7021)

PVC filler 20 20

(Solvic 266 SF)

Isopropylated triaryl phosphate 60 60

(Reofos 50) C -C dialkyl phthalate ^' 10 10 Santicizer 711)

Butyl-tin stabiliser 2 2

(Lankro LT 63)

i0₂ (Tioxide RFC 5) 2 2

2-dibutylamino-4,6-dithiol- 2 2 s-triazine

MgO 2 3

Viscosity at Shear Rate D of 5200 5300

10 s^"1 (mPa.s)

The compositions were pre-gelled by heating at 100°C for 10 minutes and were cured in a mould under a pressure of 30 kg/cm² at 170°C for 10 minutes. The cured compositions were removed from the mould without cooling.

Further samples of compositions II.a were subjected to the same pre-gelling and curing process except that the cure temperature was 160°C and 150°C respectively.

The % Swelling and % Gel of the compositions, measured as described in Example I, were as follows:

% Swelling % Gel

Composition II.a - Cure at 170°C +466 100

Composition II.a - Cure at 160°C +468 100

Composition II.a - Cure at 150°C +52 58

Composition II.b - Cure at 170°C +321 100 The compositions II.a and II.b were tested on an oscillating disc rheometer (Monsanto Rheograph) . The resulting plot of torque against time for curing at 170°C during 120 minutes showed that^" both compositions had substantially the same degree and rate of cure at 170°C, the maximum torque being 26.2 in.lb (2.96 N.m. ) . j

Mechanical properties of composition II.a and of a similar composition in which the MgO and 2-dibutylamino-4,6-dithiol-s-triazine were omitted (composition II.c) , both cured at 170°C, were as follows:

II.a II.c Tensile Strength, DIN 53504 (MPa) 15.5 15.6 Elongation at Break, DIN 53504 (%) 317 398 300% Modulus, DIN 53504 (MPa) 14.7 12.3 Shore A Hardness,^' DIN 53505 (°) 68 66 Abrasion Resistance, DIN 53516 (mm³) 115 123 Limiting Oxygen Index (%0„) 29.2 26.9

Observations from the above experiments include the following in relation to compositions containing a 6:1 phosphate:phthalate piasticizer:

(i) The resulting viscosity is less than half that of a composition containing only a- phosphate as the piasticizer (Example I, composition I.e); ^' - ' •

(ii) The compositions undergo a highly efficient cure even with low levels of MgO and triazine derivative;

(iii) No crosslinking occurs during the mixing and pre-gelling stages;

(iv) At cure temperatures above 160°C no fluxing of the composition is observed and the cured composition can be removed from the mould without cooling;

(v) 300% moduϋus and abrasion-resistance are increased by use of MgO and the triazine derivative;

(vi) Limiting oxygen index is increased by use of MgO and the triazine derivative; it increases in greater than 2% 0„ and imparts a high level of flame retardancy. EXAMPLE III Paste compositions were prepared from the following formulations:

III.a ^" Ill.b III.c

(parts by weight)

PVC icrosuspension (Vinnol P 70) 100 100 100

Diphenyl cresyl phosphate 60 60 60 (Disflamoll DPK)

C_-C₈ dialkyl phthalate 10 10 10

(Reomoll L 79)

Epoxidised soya oil (Edenol D 81) 5 5 5

Non-ionic fatty acid ester 5 5 5 derivative (Atmer 154)

Butyl-tin stabiliser (Lankro LT 63) 2 2 2

MgO 2 2 2

2-dibutylamino-4,6-dithiol- 2 0 0 s-triazine

2,4,6-trithiol-s-triazine 0 2 2

Antimony trioxide 5 5 5

Alumina trihydrate 0 0 10

Viscosity at Shear Rate D 3500 3600 4200 10 s (mPa.s)

The compositions were pre-gelled by heating at 100°C for 10 minutes and were cured in a mould under a pressure of 30 kg/cm² at 170°C for 10 minutes. The cured compositions were removed from the mould at 120°C. Physical properties of the cured compositions were as follows:

III-a Ill.b III. c

% Gel, measured as in Example I 100 100 100

Shore A Hardness, DIN 53505 (°) 70 67 69

Abrasion Resistance, DIN 53516 141 170 199 (mm³ ) Limiting Oxygen Index (%0„) 30.7 30.8 32.4

Surface Resistivity, _fi 4.7 3.3 6.0 DIN 22104 (ohm), x 10^a

Composition Ill.b was tested on an oscillating disc rheometer (Monsanto Rheograph) . The plot of torque against time for curing at 170°C during 120 minutes resulted in a curve showing a maximum torque of 14.9 in.lb(l.θ8 N.m.).

These experiments illustrate the employment of solid flame- retardant additives. The paste viscosity is satisfactory and the cured compositions exhibit a high level of limiting oxygen index. The compositions are particularly suitable for conveyor belting to be employed in underground situations where flame-resistance is important.

EXAMPLE IV

5 Paste compositions were prepared from the following basic formulation incorporating various amounts of butyl-tin stabiliser:

Parts by weight

PVC microsuspension (Vestolit B 7021) 100

Isopropylated triaryl phosphate 80

10 (Reofos 50)

Chlorinated paraffin (Cereclor 52 S) 10

Alumina trihydrate 20

Antimony trioxide 5

Non-ionic fatty acid ester derivative 3

15 (At er 154)

Triazine derivative - 2

Butyl-tin stabiliser (Lankro LT 63) Various

Two sets of compositions were prepared, one set containing

2,4 _r6-trithiol-s-triazine and the other set containing 2-dibutylamino-

20 4,6-dithiol-s-triazine as the triazine derivative.

The compositions were pre-gelled by heating at 120"C for 10 minutes and were cured in a mould at 170°C for 10 minutes. The cured compositions were removed from the mould at 80°C.

Physical properties of the cured compositions were as follows:

25 Employing 2,4,6-trithiol-s-triazine

Amount of Butyl-Tin Stabiliser (Parts by Weight) : _0_ λ "_ _4 _6 10

% Swelling, measured as in Example I 117 389 549 534 41

% Gel, measured as in Example I 36.1 88.3 100 100 8

Abrasion Resistance, DIN 53516 (mm³) 217 203 ' 202 202 21

^' 30 Limiting Oxygen Index (%0₂) 29.2 31.2 35.8 33.7 30

Employing 2-d_U3utylamino-4,6-dithiol-s-triazine

Amount of Butyl-Tin Stabiliser (Parts by Weight): _2 4. 6 . 1

% Swelling, measured as -in Example I 108 300 175 115 6

% Gel, measured as in Example I 35.7 78.6 51.4 36.72

35 Abrasion Resistance, DIN 53516 (mm³) 206 200 208 219 2

Limiting Oxygen Index (JέO,) 29.6 31.9 30.1 28.72

Also, the above experiment employing 2,4,6-trithiol-s-triazine and

4 parts by weight of butyl-tin stabiliser was repeated except that octyl diphenyl phosphate was employed in place of the isopropylated triaryl phosphate. The product exhibited a 100% gel content and had other satisfactory properties.

This Example illustrates the coupling effect of an organo-tin stabiliser", a phosphate piasticizer and a triazine derivative in MgO-free compositions to produce cured products having a high level of flame retardancy, particularly ,when employing 2,4,6-trithiol-s-triazine.

EXAMPLE V A paste composition was prepared from the basic formulation given in Example IV wherein the triazine derivative is 2,4,6-trithiol-s-triazin and the amount of the butyl-tin stabiliser is 4 parts by weight, and additionally 2 parts by weight of azodicarbonamide were included in the composition.

The composition was pre-gelled by heating at 120°C for 10 minutes and, after complete de-aeration, was cured in a mould by heating at 180°C for 10 minutes^' in a hot-air oven. The cured composition was removed from the mould at 50°C.

The product was a cellular material having a density of about 1.1 g/cm³ and was insoluble in tetrahydrofuran even after 48 hours immersion. The product may be employed in, for example, floor coverings.

EXAMPLE VI A solid-woven polyester textile fabric of tensile strength at least 315 N/mm (Code EE 315 t) was impregnated by dipping in composition II.a (Example II) having a viscosity of 5400 mPa.s measured at a shear rate D of 10 s~ , and the i pregnant was pre-gelled at 100°C for 10 minutes. Both faces of the pre-gelled impregnated fabric were skim- coated with a rubber composition and then a rubber cover layer was applied to the coatings. The composite was then heated at 160°C for 10 minutes in a press-mould under a pressure of 30 kg/cm². When the composite was removed from the press-mould at 100 °C and at 120°C, the product was strong and stable and suitable for use as conveyor belting.

EXAMPLE VII A solid-woven polyester/polyamide textile fabric of tensile strength at least 1250 N/mm (Code EP 1250 T) was impregnated and coated with compositions prepared from the basic formulation given in Example IV wherein the triazine derivative is 2,4,6-trithiol-s-triazine and the amount of the butyl-tin stabiliser is 4 parts by weight. The impregnant 14. composition had a viscosity of 6600 mPa.s at a shear rate D of 10 s~ . The impregnated and coated fabric was pre-gelled in an oven at 130^βC and was then heated at 165°C for 25 minutes in a press-mould under a pressure of 30 kg/cm². The resulting composite was removed from the press-mould at a temperature well above the de-moulding temperatures normally required in the production of conventional pvc conveyor belting.

The product was an antistatic high safety-level belt material having the following properties:- Thickness: 14.1 mm; Weight: 20.6 kg/m²;

Surface Resistivity, DIN 22104: 0.3 x 10 ohm; Abrasion Resistance, DIN 53516: 134 mm³.

In addition, the product passed the following standard safety tests:- - Flame Test according to ISO R 340, DIN 22103, NCB 158, MSHA and NFT 47-108 Gallery Test according to DIN 22118;

Propane Gallery Test according to CEE and NCB specifications; Drum Friction Test according to CEE and NCB specifications.

In the Drum Friction Test the maximum temperature measured was below 270°C_V compared to 280-290°.Ofor. conventional pvc conveyor belting.

Claims

CLAIMS :

1. Curable composition comprising a vinyl chloride polymer, a piasticizer and a triazine derivative selected from 2-substituted-4,6- dithiol-s-triazines and salts thereof, characterised in that the piasticizer comprises a phosphate piasticizer.

2. Composition according to Claim 1 wherein the phosphate piasticizer has at least two aryl and/or alkaryl groups.

3. Composition according to Claim 1 or 2 wherein the phosphate piasticizer is selected from isopropylated triaryl phosphate, diphenyl cresyl phosphate and octyl diphenyl phosphate.

4. Composition according to any one of the preceding Claims which includes a non-phosphate piasticizer.

5. Composition according to Claim 4 wherein the phosphate:non- phosphate piasticizer ratio is in the range 95:5 to 80:20 by weight.

6. Composition according to Claim 4 or 5 wherein the non-phosphate piasticizer is an alkyl phthalate piasticizer.

7. Composition according to any one of the preceding Claims wherein the total amount of piasticizer is in the range 40 to 120 parts by weight per 100 parts by weight of vinyl chloride polymer.

8. Composition according to any one of the preceding Claims which includes an organo-tin stabiliser.

9. Composition according to Claim 8 wherein the organo-tin stabiliser is an alkyl-tin stabiliser.

10. Composition according to Claim 9 wherein the alkyl-tin stabiliser is a butyl-tin stabiliser.

11. Composition according to Claim 8, 9 or 10 wherein the amount of organo-tin stabiliser is in the range 0.5 to 8 parts by weight per 100 parts by weight of vinyl chloride polymer.

12. Composition according to any one of the preceding Claims which includes a basic metal compound.

13. Composition according to Claim 12 wherein the amount of basic metal compound is in the range 2 to 10 parts by weight per 100 parts by weight of vinyl chloride polymer.

14. Composition according to any one of the preceding Claims which includes magnesium oxide.

15. Composition according to any one of the preceding Claims which includes one or more solid flame-retardants in an amount of up to 30 parts by weight per 100 parts by weight of vinyl chloride polymer.

16. Composition according to any one of the preceding Claims which includes antimony trioxide and/or alumina trihydrate.

17. Composition according to any one of the preceding Claims which includes a liquid flame-retardant.

18. Composition according to any one of the preceding Claims which includes a chemical blowing agent.

19. Composition according to Claim 18 wherein the chemical blowing agent is azodicarbonamide.

20. Composition according to any one of the preceding Claims which includes an onium salt.

21. Composition according to any one of the preceding Claims wherein the triazine derivative is 2,4,6-trithiol-s-triazine and/or a salt thereof

22. Composition according to any one of Claims 1 to 20 wherein the triazine derivative is a 2-(tertiary amino)-4,6-dithiol-s-triazine and/or a salt thereof.

23. Composition according to Claim 22 wherein the triazine derivative is 2-dibutylamino-4,6-dithiol-s-triazine and/or a salt thereof.

24. Composition according to any one of Claims 1 to 20 wherein the triazine derivative is a 2-substituted-4,6-dithiol-s-triazine and/or a salt thereof, the 2-substituent-being selected from -NHC,H_, b Z>

- (C₂H₅)₂, -N(CH₃)₂, - (CH₂CgH₅)₂ and -CCgH₅.

25. Composition according to any one of the preceding Claims wherein the amount of triazine derivative is in the range 2 to 6 parts by weight per 100 parts by weight of vinyl chloride polymer.

26. Composition according to any one of the preceding Claims which is a paste or plastisol having a viscosity in the range 3000 to 8000 mPa.s at a shear rate D of 10 s at 20°C .

27. Composition according to any one of the preceding Claims which includes an additional polymer which is curable by the triazine derivative.

28. Method of making a cured product characterised by subjecting a composition as defined in any one of the preceding Claims to curing conditions.

29. Method according to Claim 28 wherein the composition is subjected to curing conditions in a mould and the cured product is removed from the mould at a temperature of at least 60°C.

30. Composition according to any one of Claims 1 to 27 or Method according to Claim 28 or 29 wherein the composition is present as an impregnant in and/or coating on a textile fibre carcass.

31. Method according to Claim 28, 29 or 30 wherein the composition is pre-gelled by heating to solidify the composition without attaining its maximum mechanical properties, and subsequently is subjected to final curing conditions.

32. Method according to Claim 31 wherein the composition is pre- gelled by heating in the range 80°C to 150°C.

33. Method according to Claim 31 or 32 wherein the composition is subjected to final curing conditions at a temperature of at least 160°C.

34. Method according to any one. of Claims 28 to 33 wherein the cured product is removed from the mould at a temperature of at least 120°C.

35. Method according to any one of Claims 28 to 34 wherein the cured product is removed from the mould at a temperature of up to 180°C.

36. Moulded product made by a method according to any one of Claims 28 to 35.

37. Moulded product according to Claim 36 which is a carcass for mechanical belting, especially conveyor belting.

38. Moulded product according to Claim 36 or 37 having a maximum temperature of less than 2,70°C in the standard Drum Friction Test according to CEE and NCB specifications.